Policy control architecture has been defined by 3rd Generation Partnership Project (3GPP). Policy elements can maintain information on active packet connections of users and about packet gateways via which the packet connections traverse.
Traffic detection function (TDF), based on packet inspection, can be applied in a network to support policy and charging control for services for which the policy and charging control function (PCRF) does not get related service information from an application function (AF) or proxy call state control function (P-CSCF).
A standalone TDF is not able to identify the establishment of a packet data connection, because the GPRS tunneling protocol (GTP) operates between the PCEF and the access network and is consequently not seen by the standalone TDF.